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Abstract

Disturbances shape forest structure and composition, but the temporal dynamics of disturbance patterns, their influence on dynamics of forest structural complexity, and the potential impacts of ongoing climate changes are not fully understood. We addressed these issues by focusing on (1) long-term, landscape level retrospective analysis of disturbance dynamics of mountain Norway spruce (Picea abies) forest; (2) testing for the prevailing disturbance agent; and (3) the detection of disturbance drivers, particularly site conditions, using a dendrochronological approach.

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... Recent natural disturbances in Central and Eastern European mountain spruce forests have caused extensive mortality across large areas in a few landscapes, while other regions have been subject to more localized smallor moderate-scale events (Senf and Seidl 2018). Likewise, plot-and stand-level dendrochronological reconstructions suggest that mixed-severity disturbance regimes with wide variation of low to high disturbance severities historically operated in mountain spruce forests , Trotsiuk et al. 2014, Cada et al. 2016. The prevailing disturbance agents are windstorms and bark beetle (Ips typhographus) outbreaks ( Cada et al. 2016, Senf andSeidl 2018), although beetle disturbances are often triggered by windthrow events and local weather conditions, particularly droughts. ...
... 2020; Schurman et al. 2018). Data were compiled from published regional studies across a large geographical gradient covering the Carpathian Mountains of southern and northern Romania , Ukraine (Trotsiuk et al. 2014), southern and northern Slovakia (Janda et al. 2017), the Bohemian Forest in the Czech Republic ( Cada et al. 2016), and the Harz Mountains in Germany (Meyer et al. 2017;Fig. 1). ...
... Stands with no evidence of direct human influence, such as logging or livestock grazing, were selected with the help of local experts or primary forest inventories (Mikol a s et al. 2019). In stands of the Bohemian Forest, the prevailing influence of natural disturbances was evident by the significant association of reconstructed events and windstorm and bark beetle (Ips typographus) outbreak events in historical records (see Cada et al. 2016 for more details about possible human influence in these stands). ...
Article
Estimates of historical disturbance patterns are essential to guide forest management aimed at ensuring the sustainability of ecosystem functions and biodiversity. However, quantitative estimates of various disturbance characteristics required in management applications are rare in longer‐term historical studies. Thus, our objectives were to: (1) quantify past disturbance severity, patch size, and stand proportion disturbed, and (2) test for temporal and sub‐regional differences in these characteristics. We developed a comprehensive dendrochronological method to evaluate an approximately two‐century‐long disturbance record in the remaining Central and Eastern European primary mountain spruce forests, where wind and bark beetles are the predominant disturbance agents. We used an unprecedented large‐scale nested design dataset of 541 plots located within 44 stands and 6 sub‐regions. To quantify individual disturbance events, we used tree‐ring proxies, which were aggregated at plot and stand levels by smoothing and detecting peaks in their distributions. The spatial aggregation of disturbance events was used to estimate patch sizes. Data exhibited continuous gradients from low‐ to high‐severity and small‐ to large‐size disturbance events. In addition to the importance of small disturbance events, moderate‐scale (25‐75% of the stand disturbed, >10 ha patch size) and moderate‐severity (25‐75% of canopy disturbed) events were also common. Moderate disturbances represented more than 50% of the total disturbed area and their rotation periods ranged from one to several hundred years, which is within the lifespan of local tree species. Disturbance severities differed among sub‐regions, whereas the stand proportion disturbed varied significantly over time. This indicates partially independent variations among disturbance characteristics. Our quantitative estimates of disturbance severity, patch size, stand proportion disturbed, and associated rotation periods provide rigorous baseline data for future ecological research, decisions within biodiversity conservation, and silviculture intended to maintain native biodiversity and ecosystem functions. These results highlight a need for sufficiently large and adequately connected networks of strict reserves, more complex silvicultural treatments that emulate the natural disturbance spectrum in harvest rotation times, sizes, and intensities, and higher levels of tree and structural legacy retention.
... Disturbances reduce canopy cover and the associated reduction in competition permits formerly suppressed trees to recruit into the canopy stratum. The disturbance history of a forest stand can therefore be reconstructed from growth rate anomalies suggestive of canopy accession dates, which are naturally cataloged in tree-ring series (Lorimer & Frelich, 1989 ( Cada et al., 2016;Janda et al., 2017;Svoboda et al., 2010;Trotsiuk et al., 2014) was compiled into a regional chronology to quantitate historical primary Picea abies (L. H. Karst.) ...
... Disturbance histories were reconstructed with tree cores collected from primary mountain P. abies forest inventory plots, located with assistance from managers of protected areas and knowledge of other local experts throughout the Bohemian Forest in the Czech Republic ( Cada, Svoboda, & Janda, 2013;Cada et al., 2016) and the Carpathian Mountains in Slovakia (Janda et al., 2017), Ukraine (Trotsiuk et al., 2014), and northern Romania (Svoboda et al., 2014). Since the publication of these national chronologies, additional tree cores have been collected throughout southern Romania. ...
... Increasingly negative Palmer drought severity index (PDSI) values indicate more severe drought conditions, so decadal PDSI minimums (Cook et al., 2015) presented on the x axis were multiplied by À1 to better reflect higher drought severity corresponds with higher rates of canopy removal. A sigmoid response function with an inflection point at PDSI = À2.08 was fit to disturbance rates 4 | DISCUSSION Picea abies stands throughout the Bohemian Forest and the Carpathian Mountains have been shaped by disturbances ranging widely in timing, extent, and severity ( Cada et al., 2016;Janda et al., 2017;Svoboda et al., 2014). The general patterns in our reconstructed disturbance history, conducted at an unprecedented scale for European primary forests, provide insight into how variation is driven by localized vs. regional factors (Figure 1). ...
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Determining the drivers of shifting forest disturbance rates remains a pressing global change issue. Large-scale forest dynamics are commonly assumed to be climate driven, but appropriately scaled disturbance histories are rarely available to assess how disturbance legacies alter subsequent disturbance rates and the climate sensitivity of disturbance. We compiled multiple tree-ring based disturbance histories from primary Picea abies forest fragments distributed throughout five European landscapes spanning the Bohemian Forest and the Carpathian Mountains. The regional chronology includes 11 595 tree cores, with ring dates spanning the years 1750 to 2000, collected from 560 inventory plots in 37 stands distributed across a 1000 km geographic gradient, amounting to the largest disturbance chronology yet constructed in Europe. Decadal disturbance rates varied significantly through time and declined after 1920, resulting in widespread increases in canopy tree age. Approximately 75% of current canopy area recruited prior to 1900. Long-term disturbance patterns were compared to an historical drought reconstruction, and further linked to spatial variation in stand structure and contemporary disturbance patterns derived from LANDSAT imagery. Historically, decadal Palmer drought severity index minima corresponded with higher rates of canopy removal. The severity of contemporary disturbances increased with each stand's estimated time since last major disturbance, increased with mean diameter and declined with increasing within-stand structural variability. Reconstructed spatial patterns suggest that high small-scale structural variability has historically acted to reduce large-scale susceptibility and climate sensitivity of disturbance. Reduced disturbance rates since 1920, a potential legacy of high 19th century disturbance rates, have contributed to a recent region-wide increase in disturbance susceptibility. Increasingly common high-severity disturbances throughout primary Picea forests of Central Europe should be reinterpreted in light of both legacy effects (resulting in increased susceptibility) and climate change (resulting in increased exposure to extreme events). This article is protected by copyright. All rights reserved.
... Tropical hurricanes are one of the main factors of natural disturbance, because they severely influence the state, structure, functioning, and composition of ecosystems (Cada et al., 2016;Gill, Jarvis, Veblen, Pickett, & Kulakowski, 2017;Manson & Jardel, 2009), cause species mortality, and generate opportunities for native and invasive species to establish themselves (Cada et al., 2016). Damage caused by tropical hurricanes depends on factors such as proximity, duration, precipitation, wind speed, and biotic and abiotic factors (Doyle, Krauss, & Wells, 2009). ...
... Tropical hurricanes are one of the main factors of natural disturbance, because they severely influence the state, structure, functioning, and composition of ecosystems (Cada et al., 2016;Gill, Jarvis, Veblen, Pickett, & Kulakowski, 2017;Manson & Jardel, 2009), cause species mortality, and generate opportunities for native and invasive species to establish themselves (Cada et al., 2016). Damage caused by tropical hurricanes depends on factors such as proximity, duration, precipitation, wind speed, and biotic and abiotic factors (Doyle, Krauss, & Wells, 2009). ...
... Los ciclones tropicales son uno de los principales factores de disturbios naturales, ya que influyen severamente en el estado, estructura, funcionamiento y composición de los ecosistemas (Cada et al., 2016;Gill, Jarvis, Veblen, Pickett, & Kulakowski, 2017;Manson & Jardel, 2009), causan mortalidad de especies y generan oportunidades de establecimiento para las especies nativas e invasoras (Cada et al., 2016). Los daños ocasionados por los ciclones tropicales dependen de factores como la cercanía, duración, precipitación, velocidad del viento y factores bióticos y abióticos (Doyle, Krauss, & Wells, 2009). ...
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Introduction: Tropical hurricanes modify composition and structure of ecosystems. Objective: To analyze the impact of tropical hurricanes on the recovery and resilience of vegetation cover.Materials and methods: The resilience of the lower basin and estuary of San Jose del Cabo was evaluated by studying the impact of 11 tropical hurricanes (2013-2017) on the vegetation cover. Landsat images were analyzed for each event and two SPOT-6 images for the Hurricane Lidia. The areas of gain, stability, loss and recovery of vegetation types were estimated based on the analysis of changes in the Normalized Difference Vegetation Index (NDVI).Results and discussion: Average stability of vegetation cover was 90 %; however, in the case of hurricane Odile (2014) and Lidia (2017), stability decreased considerably, with a loss of 35.4 and 20.5 %, respectively, being the perennial herbaceous vegetation the most affected. One year after Odile and Lidia, recovery was 8.4 % and 25.4 %, respectively; the most recovered vegetation type was reed-tree. The analysis of SPOT-6 images allowed the detailed observation of Lidia's effect on palm grove. The main cause of its loss was runoff from the stream, which favored the growth of invasive species (Arundo donax L. and Tamarix sp.); furthermore, it was estimated that 1.4 ha were deforested, and an area of 20 ha affected by fire in 2017.Conclusion: Vegetation is resilient to tropical hurricanes; however, events that provide more than 50 % of annual precipitation decrease the capacity of vegetation to recover.
... The life cycle dynamics of these forest ecosystems is driven by a specific disturbance regime, which is in some aspects more similar to the dynamics of northern boreal forests than of the temperate mixed and deciduous forests in lower elevations. In old-growth, spruce-dominated mountain forests, stand-replacing disturbances are characteristically caused by abiotic (e.g., windstorm) and biotic (typically an outbreak of spruce bark beetles: Ips typographus L., Ips duplicatus Sahlberg) factors [2,3]. Although fire events cannot be excluded in general, these were common, particularly in early and middle Holocene [4,5]. ...
... Occasional uprooting and breaking of single to several trees or the whole-stand disturbance during storms usually followed by an outbreak of bark beetles can result in canopy openings on scales from small gaps in the size of fractions of a hectare to large areas spanning over thousands of hectares [6][7][8][9]. The disturbance regime of mountain spruce forests shapes their physiognomy, spatial structure, pedocomplexity and even the landform form [10] by enabling re-occurrence of early phases of forest succession and their further development towards the re-establishment of the old-growth forest [3]. ...
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Stand-replacing disturbances are a key element of the Norway spruce (Picea abies) forest life cycle. While the effect of a natural disturbance regime on forest physiognomy, spatial structure and pedocomplexity was well described in the literature, its impact on the microbiome, a crucial soil component that mediates nutrient cycling and stand productivity, remains largely unknown. For this purpose, we conducted research on a chronosequence of sites representing the post-disturbance development of a primeval Norway spruce forest in the Calimani Mts., Romania. The sites were selected along a gradient of duration from 16 to 160 years that ranges from ecosystem regeneration phases of recently disturbed open gaps to old-growth forest stands. Based on DNA amplicon sequencing, we followed bacterial and fungal community composition separately in organic, upper mineral and spodic horizons of present Podzol soils. We observed that the canopy opening and subsequent expansion of the grass-dominated understorey increased soil N availability and soil pH, which was reflected in enlarged bacterial abundance and diversity, namely due to the contribution of copiotrophic bacteria that prefer nutrient-richer conditions. The fungal community composition was affected by the disturbance as well but, contrary to our expectations, with no obvious effect on the relative abundance of ectomycorrhizal fungi. Once the mature stand was re-established, the N availability was reduced, the pH gradually decreased and the original old-growth forest microbial community dominated by acidotolerant oligotrophs recovered. The effect of the disturbance and forest regeneration was most evident in organic horizons, while the manifestation of these events was weaker and delayed in deeper soil horizons.
... A study in the Carpathian mountains found a higher disturbance rate in forests established after 1860 compared to "old" forests (Munteanu et al., 2015). These "new" forests may be more susceptible to natural disturbances due to their homogeneous species composition and uniform age structure (Munteanu et al., 2015;Seidl et al., 2011b), as a high disturbance rate in recent years has also been observed in primary and unmanaged spruce stands that developed after major disturbances 19 th century (Čada et al., 2016;Janda et al., 2017;Panayotov et al., 2015). However, a higher disturbance rate in "new" forests could also be the result of different management strategies (e.g., clear ...
... Bebi et al. (2017) analysed the difference in structure between pre-and post-1880 forests in NFI plots across Switzerland, and found that "new" forests do not only have a lower total growing stock, but are also vertically more homogeneous. In unmanaged mountain spruce forests in Central and Eastern Europe, uniform stands established after large disturbance events in the mid-19 th century are now experiencing a new pulse in disturbances (Čada et al., 2016;Janda et al., 2017;Panayotov et al., 2015). In our study, homogeneous spruce stands established only 80-100 years ago are most susceptible to disturbances. ...
... (Pickett & White, 1985). Disturbances, such as windthrow, insect infestation, flooding, or fire, are a significant element of the natural forest dynamic (Čada et al., 2016;Nagel & Diaci, 2006;Nagel et al., 2007), and forestry activities are deemed to be close-to-nature if they are analogous to natural disturbances (Long, 2009;Seymour et al., 2002). With ongoing climate change, disturbance patterns may change, with an increase in disturbance frequency and/or intensity likely in some areas (Seidl et al., 2017). ...
... Wind is the most important natural disturbance agent in Central Europe (Čada et al., 2016;Gardiner et al. 2010), and to date the most researched. In particular, the storms "Vivian and Wiebke" in February 1990 gave rise to intense research effort on windthrow in Switzerland and Germany (Fischer & Fischer, 2009;Nationalparkverwaltung Bayerischer Wald, 2001;Schönenberger et al., 1995;Wohlgemuth & Kramer, 2015). ...
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On the basis of long-term surveys of permanent plots and traps, we examined the communities of saproxylic beetles, fungi, herbs, and trees on an untreated 22 ha large beech forest windthrow and asked whether the results lend support to the intermediate disturbance hypothesis (IDH). We studied species richness and the similarity of community composition. Additionally, we grouped species by their frequency trend over time to successional model types to examine whether, corresponding to the IDH, the diversity of these groups explained peak richness at intermediate intervals after the disturbance. In line with the IDH, species richness showed a hump-backed temporal course for alpha and gamma diversity. We found evidence for a linear succession directly after the disturbance. This, however, did not continue, and in all species groups, a partial recovery of the initial community was observed. In the case of fungi, herbs, and trees, but not for saproxylic beetles, alpha diversity was driven by the diversity of the successional model types. Our results underline that the mechanisms driving species richness after disturbances are more complex than the IDH suggests and that these mechanisms vary with species group. We assumed that, besides competition, legacy effects, facilitation, habitat heterogeneity, and random saturation of the species pool are important. In case of trees and herbs, we found indications for strong legacy and competition effects. For fungi and beetles, substrate heterogeneity and microclimate were assumed to be important. We concluded that disturbances contribute to increasing species richness not only by reducing the effectiveness of competitors but also by increasing the amount and diversity of resources, as well as their rate of change over time.
... In natural mountain Picea abies forests, the dominant high-elevation forest type of the Carpathian Mountains, the disturbance regime is typically characterized as mixedseverity (a wide range of severities is evident in the disturbance regimes of our studied stands) , Schurman et al., 2018. Windstorms and bark beetles are the primary natural disturbance agents, and disturbances typically recur at relatively short intervals (years to decades) and cause tree mortality at relatively small scales (< 1 ha), although larger events with low frequency of 10 s to 100 s of hectares have also been documented , Čada et al., 2016. ...
... In most cases, the primary forests have remained unmanaged due to difficulty of access. These unmanaged forests are not necessarily in an advanced developmental phase because some of them may have been affected by recent natural disturbances (primarily by wind and the European spruce bark beetle; Ips typographus) that caused tree mortality at scales ranging from individual trees to dozens or even hundreds of hectares (Mueller et al., 2008;Svoboda et al., 2014;Čada et al., 2016). ...
Article
Disentangling the importance of developmental vs. environmental drivers of variation in forest biomass is key to predicting the future of forest carbon sequestration. At coarse scales, forest biomass is likely to vary along major climatic and physiographic gradients. Natural disturbance occurs along these broad biophysical gradients, and depending on their extent, severity and frequency, could either amplify or dampen spatial heterogeneity in forest biomass. Here we evaluate spatial variation in the basal area of late-successional Picea abies (L./Karst.) forests across the Carpathian Mountain Range of central Europe and compare the roles of coarse-scale biophysical gradients and natural disturbances in driving that variation across a hierarchy of scales (landscapes, stands, and plots). We inventoried forest composition and structure, and reconstructed disturbance histories using tree cores collected from 472 plots nested within 30 late-successional stands, spanning the Carpathian Mountains (ap-proximately 4.5 degrees of latitude). We used linear mixed-effects models to compare the effect of disturbance regimes and site conditions on stand basal area at three hierarchical scales. We found that the basal area of late-successional Picea abies forests varied across a range of spatial scales, with climatic drivers being most important at coarse scales and natural disturbances acting as the primary driver of forest heterogeneity at fine scales. For instance, the stand-level basal area varied among landscapes, with the highest values (48-68 m 2 ha −1) in the warmer southern Carpathian Mountains, and lower values (37-52 m 2 ha −1 on average) in cooler areas of the eastern and western Carpathians. Finer-scale variation was driven by local disturbances (mainly bark beetle and windstorms) and the legacies of disturbances that occurred more than a century ago. Our findings suggest that warming could increase the basal area of northern sites, but potential increasing disturbances could disrupt these environmental responses.
... Recurrent hurricanes can create a complex landscape pattern consisting of forest patches of varying ages and sizes at different forest successional stages. In some cases, large wind disturbances may trigger different forest successional pathways and impede a forest landscape from reaching an equilibrium state (Nagel et al. 2014;Čada et al. 2016). ...
... Landscapes in southern and western Changbai Mt. never reached an equilibrium as the proportions of different successional stages were constantly changing. Nonequilibrium for landscapes experiencing infrequent and large disturbances (e.g., hurricanes, wildfires) has been widely reported in other studies (Baker 1989;Nagel et al. 2014;Čada et al. 2016). Notably, the effects of typhoon disturbances on landscape patterns gradually stabilized after 1960, which suggested that with longer timeframe the landscape will continue to shift toward a quasi-equilibrium condition, having less area in recovered patches and more area in recovering patches than those of northern Changbai Mt. ...
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Context Study of interplay of disturbance and forest succession is key to understand forest landscape dynamics, especially under changing climate and disturbance regimes. However, most such studies are from small spatial and temporal scales, and thus may be limited to generalize at large scales. Objectives We investigate how typhoons affected forest dynamics at stand and landscape scales, whether the impacts differ among forest biomes, and whether a post-volcanic forest landscape could ultimately reach equilibrium under typhoon disturbances. Methods We used landscape modelling to spatially reconstruct the time-series (1710–2010) for the post-volcanic-eruption forest landscapes driven by forest succession and typhoon in Changbai Mountain, China. We compared aboveground biomass (AGB), climax tree species importance value, degree of recovery, and landscape pattern between northern (with typhoons) and southern and western Changbai Mt. (without typhoons). Results The effects of typhoon disturbances were minimal when forests were young (before ~1810) but gradually increased as tree grew and forest recovered. The response of forest biomes to typhoon varied, which can be attributed to individual species traits. With recurring typhoons landscape did not reach an equilibrium until 2010. However, the effects of typhoons on landscape pattern gradually stabilized after 1960, suggesting landscapes with typhoons may eventually reach a steady state. Conclusions Typhoons have long-lasting and cumulative effects that varied with successional-stages and forest biomes. Landscape under infrequent, large disturbances is nonequilibrium in the short term, but may ultimately reach equilibrium over long time periods. Historical landscape reconstruction reveals fuller spectrum of interplays of typhoons and succession.
... However, in all types, residual live trees, both dispersed and aggregated in patches, typically persisted post-fire (Berglund and Kuuluvainen 2021). Wind disturbances are also a dominant structuring process across all European forests, though varying greatly in intensity and frequency, for example exhibiting periods when high intensity wind storms are of greater prevalence (Zielonka et al. 2009;Svoboda et al. 2012Svoboda et al. , Čada et al. 2016. Recent research on the role of intermediate severity disturbances suggests a much broader range of variability in the resulting stand age class structure and tree demography than previously recognized for European forests (Nagel et al. 2014, Trotsiuk et al. 2014, Janda et al. 2017. ...
... Forests dominated by Scots pine, of which more than half are in Poland, are predominantly managed by clearcutting systems. Regional studies from the Carpathians, Rila Mountains (Bulgaria), and Bohemia (Czech Republic) suggest that mixed-severity disturbance regimes with wide variation of low to high disturbance severities historically operated in temperate mountain spruce forests (Panayotov et al. 2011, Szewczyk et al. 2011, Trotsiuk et al. 2014, Čada et al. 2016, Janda et al. 2017, Frankovič et al. 2021. We showed that this variability is not emulated by contemporary forest management. ...
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In Europe, forest management has controlled forest dynamics to sustain commodity production over multiple centuries. Yet over‐regulation for growth and yield diminishes resilience to environmental stress as well as threatens biodiversity, leading to increasing forest susceptibility to an array of disturbances. These trends have stimulated interest in alternative management systems, including natural dynamics silviculture (NDS). NDS aims to emulate natural disturbance dynamics at stand and landscape scales through silvicultural manipulations of forest structure and landscape patterns. We adapted a “Comparability Index” (CI) to assess convergence/divergence between natural disturbances and forest management effects. We extended the original CI concept based on disturbance size and frequency by adding the residual structure of canopy trees after a disturbance as a third dimension. We populated the model by compiling data on natural disturbance dynamics and management from 13 countries in Europe, covering four major forest types (i.e., spruce, beech, oak, and pine‐dominated forests). We found that natural disturbances are highly variable in size, frequency, and residual structure, but European forest management fails to encompass this complexity. Silviculture in Europe is skewed towards even‐aged systems, used predominately (72.9% of management) across the countries assessed. The residual structure proved crucial in the comparison of natural disturbances and silvicultural systems. CI indicated the highest congruence between uneven‐aged silvicultural systems and key natural disturbance attributes. Even so, uneven‐aged practices emulated only a portion of the complexity associated with natural disturbance effects. The remaining silvicultural systems perform poorly in terms of retention as compared to tree survivorship after natural disturbances. We suggest that NDS can enrich Europe's portfolio of management systems, for example where wood production is not the primary objective. NDS is especially relevant to forests managed for habitat quality, risk reduction, and a variety of ecosystem services. We suggest a holistic approach integrating natural dynamics silviculture with more conventional practices.
... In deciduous forest understoreys, seasonal canopy phenology causes large changes in light quality and irradiance through the year that potentially produce complex effects on litter decompostion (Pierist e et al., 2019(Pierist e et al., , 2020a. Canopy gap dynamics created by a variety of natural or human disturbances ( Cada et al., 2016), produce heterogeneous light environments in a forest that partially drive species diversity (Wang et al., 2020). This leads to variation in leaf structural and biochemical functional traits (e.g. ...
... Global forests cover about 31% of the land area and their vegetation and soil contain nearly half of the terrestrial biosphere C stock (FAO, 2020), but as nonequilibrium ecosystems they are continuously subject to a variety of disturbances, e.g. wind, landslide or logging ( Cada et al., 2016). Thus, the omission of photodegradation from classical models implies that a considerable proportion of their C loss may have not been identified (Austin & Vivanco, 2006), though identifying the relative importance of photochemical mineralization and photofacilitation requires further research. ...
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• Litter decomposition determines carbon (C) backflow to the atmosphere and ecosystem nutrient cycling. Although sunlight provides the indispensable energy for terrestrial biogeochemical processes, the role of photodegradation in decomposition has been relatively neglected in productive mesic ecosystems. • To quantify the effects of this variation, we conducted a factorial experiment in the understorey of a temperate deciduous forest and an adjacent gap, using spectral-attenuation-filter treatments. • Exposure to the full spectrum of sunlight increased decay rates by nearly 120% and the effect of blue light contributed 75% of this increase. Scaled-up to the whole forest ecosystem, this translates to 13% loss of leaf-litter C through photodegradation over the year of our study for a scenario of 20% gap. Irrespective of the spectral composition, herbaceous and shrub litter lost mass faster than tree litter, with photodegradation contributing the most to surface litter decomposition in forest canopy gaps. Across species, the initial litter lignin and polyphenolic contents predicted photodegradation by blue light and UV-B radiation, respectively. • We concluded that photodegradation, modulated by litter quality, is an important driver of decomposition, not just in arid areas, but also in mesic ecosystems such as temperate deciduous forests following gap opening.
... In Switzerland, hazel grouse is nowadays restricted to mountain forests in the Alps and partly in the Jura mountains (Maumary et al. 2007). There, the heterogeneous topography causes smallscale changes in site conditions and forest structural complexity ( Cada et al. 2016) and thus, is considered to have a high landscape potential as hazel grouse habitat. ...
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Recent studies show that light detection and ranging (LiDAR) derived habitat variables significantly increase the performance and accuracy of species distribution models (SDMs). In particular, the structure of complex habitats such as forest can be accurately parametrized by an area-wide, LiDAR-based vegetation profile. However, evidence of specific applications of such models in real-world conservation management still remains sparse. Here, we developed a resource selection SDM for hazel grouse (Bonasa bonasia L.) in a Swiss nature park with the aim to map habitat suitability and to inform the park management about habitat improvement measures. We used remote sensing, particularly LiDAR to derive ecologically relevant forest vegetation characteristics at the local scale and used them as predictors in an ensemble SDM approach. The predicted habitat suitability was mainly affected by local, fine grained vegetation structure. Average vegetation height, shrub density and canopy height variation contributed most to the habitat quality for hazel grouse. This clearly shows how LiDAR provides the means to develop ecologically interpretable predictor variables of forest habitat structure and that these predictors can be used to reliably map local-scale habitat quality, indicated by high model performance scores (median AUC of 0.918). This improves spatial conservation planning, and at the same time, provides meaningful information to derive habitat improvement measures that can be implemented in the field by foresters. Hazel grouse occurrence in the park is restricted to a few highly suitable, disjunct habitat patches. Therefore, conservation management should increase the connectivity of suitable habitat with the aim to stimulate an increase and better exchange of individuals in the regional hazel grouse population. Habitat improvements can be achieved by forestry measures that regularly integrate early successional forest stages into production forests. They should contain stands with a shrub density of around 30% as well as heterogeneous stands in terms of vegetation height. © 2017 The Authors. Remote Sensing in Ecology and Conservation published by John Wiley & Sons Ltd on behalf of Zoological Society of London
... Dendrochronologically recorded disturbances peaked in the 1820s, but became rare after 1880. In the absence of large disturbances during the twentieth century, spruce forests matured to the ages that are sensitive to windthrows and bark beetle attacks, contributing to the severity and large extent of the disturbances in the 1990s and 2000s (Brůna et al. 2013;Čada et al. 2016). ...
Chapter
The Czech Republic belongs to the temperate broad-leaved deciduous forest biome for its largest part, but two of its dry lowland areas belong to the forest-steppe biome. Landscapes corresponding to the coniferous forest biome and alpine tundra occur mainly as temperate orobiomes in small areas. Eight altitudinal vegetation belts from lowland to alpine are distinguished. There are high diversities of different vegetation types mainly in deep river valleys in the Bohemian Massif, karst areas, sandstone pseudokarst areas, on solitary volcanic hills, in glacial cirques, lowland riverine landscapes and serpentinite areas. Potential natural vegetation across most of the country is deciduous and mixed forests of beech, oak, hornbeam and noble hardwoods, and coniferous forests of spruce and fir. However, large areas of these forests have been cleared or converted into forest plantations. Open landscape is covered mainly by arable land and perennial grassland. Diversity, ecology, distribution, history and dynamics of the different vegetation types defined in the national vegetation classification are described here in detail.
... This also stresses the need to improve our understanding of the historical range of windthrow as a natural disturbance and the likely future range of its variability (FRV). The historical consequences of windthrow (including land use changes) are the topic of studies in many European regions [20,21]. In contrast, predictions of FRVs in forested landscapes have rarely been studied up to now [22], and these predictions are based on mechanistic [23] or empirical models [24]. ...
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Norway spruce dominates mountain forests in Europe. Natural variations in the mountainous coniferous forests are strongly influenced by all the main components of forest and landscape dynamics: species diversity, the structure of forest stands, nutrient cycling, carbon storage, and other ecosystem services. This paper deals with an empirical windthrow risk model based on the integration of logistic regression into GIS to assess forest vulnerability to wind-disturbance in the mountain spruce forests of Šumava National Park (Czech Republic). It is an area where forest management has been the focus of international discussions by conservationists, forest managers, and stakeholders. The authors developed the empirical windthrow risk model, which involves designing an optimized data structure containing dependent and independent variables entering logistic regression. The results from the model, visualized in the form of map outputs, outline the probability of risk to forest stands from wind in the examined territory of the national park. Such an application of the empirical windthrow risk model could be used as a decision support tool for the mountain spruce forests in a study area. Future development of these models could be useful for other protected European mountain forests dominated by Norway spruce.
... Discrete weather events, such as storms or heatwaves, are important drivers of disturbances in marine systems, where they are expected to increase in frequency and severity under most future climate change scenarios (IPCC 2014, Cai et al. 2015, Oliver et al. 2019. The response of communities and ecosystems to disturbances de -pends on characteristics of the events, such as the type, frequency, intensity and extent of disturbance (McCabe & Gotelli 2000, Sousa 2001, Benedetti-Cecchi et al. 2006, Vaselli et al. 2008, Thakur et al. 2014, Čada et al. 2016. At the same time, disturbance effects can also vary dramatically according to characteristics independent of the events, such as the specific local biotic and abiotic context (Dudgeon & Petraitis 2001, Wernberg & Connell 2008, Kramer et al. 2014. ...
Article
Disturbances often control community structure by removing large dominant species, allowing new species to colonize. Disturbances vary in intensity and extent, and their effects on resident communities can depend on local environmental conditions. We tested the effects of disturbance intensity and extent on different functional groups of understory species in kelp forests at 4 locations along an ocean climate gradient in Western Australia. We hypothesized that, compared to intact canopies, increasing disturbance intensities (50 and 100% of kelp removal) and extents (2, 4 and 8 m diameter) would promote light-dependent competitors (turf, foliose, articulated coralline and fucoid seaweeds) at the expense of less light-dependent functional groups (invertebrates and encrusting seaweeds). We also hypothesized that these effects would be most pronounced at warmer relative to cooler locations, where metabolic and ecological rates are faster. The first hypothesis was supported; light-dependent understory groups (turfs, in particular) increased, while less light-dependent groups (crusts in particular) decreased with increasing disturbance regimes. However, the second hypothesis was not supported; even though understory communities differed between locations and turf covers were highest at the warmest location, we found no significant interactions between locations and disturbance regimes. Importantly, our results revealed that even small-scale partial canopy loss can have significant effects on kelp-associated communities. The implied community-wide, density-dependent effects have implications for the management and conservation of kelp forests, because restoration of ecological functions must also consider the density of kelp forests, not simply their presence or absence.
... Natural disturbances, such as fire, wind-storms, hill-slides, avalanches, insect outbreaks and beaver activity, are important drivers of forest dynamics, maintaining structural complexity and promote a diverse species composition in both managed and unmanaged forest ecosystems (Spies and Turner, 1999). However, minimizing the risk and extent of natural disturbancesand thus the economic lossis a primary goal of forest management, which changes disturbance regimes in scale, structure and rate and alters natural gap dynamics (Cada et al., 2016;Korpel, 1995). Although forest management can mimic natural disturbances by creating small (selective cutting) or large (clear-cutting) gaps, managed forests are more homogeneous in terms of tree composition, vertical stratification, age structure and successional dynamics which can strongly affect biodiversity (Paillet et al., 2010). ...
Article
Increasing the proportion of unmanaged forests in multi-functional forest landscapes is a primary goal of international and national conservation strategies aiming at restoring natural properties in structurally simplified forests. However, the development of structural features and associated habitat suitability for forest species is largely unknown and even controversially discussed, as the development of newly established reserves is uni-directional and passes through dense maturation stages. This may negatively affect open forest species in the first phase after reserve designation. We evaluated the effects of management cessation on key habitat characteristics of four mountain forest bird species indicative of different structural components: Capercaillie (Tetrao urogallus), Hazel grouse (Bonasa bonasia), Three-toed woodpecker (Picoides tridactylus) and Pygmy owl (Glaucidium pas-serinum) across four mountain regions in Central Europe. Habitat suitability was modelled based on 300 forest sites selected independently of their management status, and predicted to an independent dataset of 42 strictly protected forest reserves in the same regions. We then compared forest reserves to managed forests with species presence or absence with regard to habitat suitability and key habitat structures and related both to the time since reserve designation. For all model species, except Pygmy owl, habitat suitability in forest reserves was significantly higher than in managed forests with species' absence, but not different from managed forests with species presence. For the species associated with open forest structures (Capercaillie, Hazel grouse, Pygmy owl) habitat suitability was significantly related to the "reserve age": reserves in the first three decades after management cessation showed a significant decrease in suitability, which increased afterwards up to the maximally recorded time of 100 years. No such correlation was found for the Three-toed woodpecker associated with deadwood and barkbeetle infestations following temporally unpredictable disturbance events. Structural characteristics varied greatly in abundance and distribution, with open structures being related to the time since reserve designation. We therefore recommend focusing on mature, near-natural and structurally diverse forests when designating new strict forest reserves.
... Rather than traditional binary classifications of infrequent, standreplacing versus frequent, gap-forming disturbances (Seymour, 2005), recent studies and management initiatives have focused on the full continuum of disturbance timing and severity, particularly intermediate-severity disturbance in temperate and boreal forests (Woods, 2004;Hanson and Lorimer, 2007;Stueve et al., 2011;Tepley et al., 2013;Nagel et al., 2014;Čada et al., 2016). These mixed-severity systems are characterized by high temporal and spatial variability of disturbance extent, frequency, and severity (e.g., tree mortality), which collectively influence forest structure and function in complex ways Tepley et al., 2013;Nagel et al., 2017;Reilly et al., 2017). ...
Article
Mixed-severity disturbance regimes are prevalent in temperate forests worldwide, but key uncertainties remain regarding the variability of disturbance-mediated structural development pathways. This study investigates the influence of disturbance history on current structure in primary, unmanaged Norway spruce (Picea abies) forests throughout the Carpathian Mountains of central and eastern Europe, where windstorms and native bark beetle outbreaks are the dominant natural disturbances. We inventoried forest structure on 453 plots (0.1 ha) spanning a large geographical gradient (\>1,000 km), coring 15–25 canopy trees per plot for disturbance history reconstruction (tree core total n = 11,309). Our specific objectives were to: (1) classify sub-hectare-scale disturbance history based on disturbance timing and severity; (2) classify current forest structure based on tree size distributions (live, dead, standing, downed); (3) characterize structural development pathways as revealed by the association between disturbance history and current forest structural complexity. We used hierarchical cluster analysis for the first two objectives and indicator analysis for the third. The disturbance-based cluster analysis yielded six groups associated with three levels of disturbance severity (low, moderate, and high canopy loss) and two levels of timing (old, recent) over the past 200 years. The structure-based cluster analysis yielded three groups along a gradient of increasing structural complexity. A large majority of plots exhibited relatively high (53\%) or very high (26\%) structural complexity, indicated by abundant large live trees, standing and downed dead trees, and spruce regeneration. Consistent with conventional models of structural development, some disturbance history groups were associated with specific structural complexity groups, particularly low-severity/recent (very high complexity) and high-severity/recent (moderate complexity) disturbances. In other cases, however, the distribution of plots among disturbance history and structural complexity groups indicated either divergent or convergent pathways. For example, multiple disturbance history groups were significantly associated with the high complexity group, demonstrating structural convergence. These results illustrate that complex forest structure – including features nominally associated with old-growth – can be associated as much with disturbance severity as it is with conventional notions of forest age. Because wind and bark beetles are natural disturbance processes that can induce relatively high levels of tree mortality while simultaneously contributing to structural complexity and heterogeneity, we suggest that forest management plans allow for the stochastic occurrence of disturbance and variable post-disturbance development trajectories. Such applications are especially appropriate in conservation areas where biodiversity and forest resilience are management objectives, particularly given projections of increasing disturbance activity under global change.
... An example of this is the mass attack of the bark beetle on spruce trees damaged by strong wind. Natural disturbances of ecosystem stability are of a recurring nature, in a longer or shorter time (e.g., Čada et al., 2016;Mitchell, 2013), which makes them the basic driving force of dynamic changes shaping the heterogenous forest structure. ...
... But in strictly protected areas where natural conditions prevail and original species composition is preserved, bark beetle is a natural part of forest dynamic, sometimes even considered as a keystone species (MÜLLER et al. 2008). These ecosystems are likely adapted to the disturbance regime (ČADA et al. 2016). After the dieback of parent stands, regeneration (stand-replacement) often depends on the amount of advanced regeneration established before the disturbance (HEURICH & JEHL 2000, MACEK et al. 2017. ...
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Natural regeneration following large-scale disturbance is a basic attribute of forest resilience. However, in the intensively managed forest ecosystems in Europe these processes are not well understood which also limits the options for silvicultural management in these ecosystems. To overcome this shortfall, we have established a large (20 ha) permanent research plot in mountain spruce forest of the Bohemian Forest Ecosystem in 2018, 20 years after one of the largest forest disturbances in Central Europe, left without forestry interventions. The spatial positions of all living trees and dead wood, including low stumps and young regeneration above 50 cm in height were recorded. In total we measured 29 464 positions of 6 species. All live individuals were tagged for permanent monitoring of mortality and growth. As a result of the data analysis the tree spatial structure of the pre-disturbance generation was more heterogeneous compared to a commercial forest. After the disturbance, it became even more heterogeneous, with very pronounced aggregation at all spatial levels, from meters to hundreds of meters. This implies that the spatial pattern of regeneration varies, even over the homogeneous environmental conditions. Explaining this large spatial variability is challenging. Current post-disturbance structure is hardly attainable by any human planting intervention. This shows the high value of non-interventional approach for nature conservation. The further purpose of the research plot is to investigate the development of the abundance and composition of species, biomass and dynamics of spatial distribution of tree individuals. The plot also offers a possibility to add further opportunities for research.
... Practical approaches in the field also differ, with some NBFM proponents only advocating selection management, while most NBFM advocates and practitioners employ a variety of silvicultural tools, including clearcutting in rare cases, and focus on tailoring interventions to site ecology, stand conditions and management objectives (Schütz 1990;Fries et al. 1998;Boncina 2011b (Nagel et al. 2013a;Čada et al. 2016). Research suggests that nature-based silvicultural systems are consistent with historical disturbance regimes of forest ecosystems (Nagel et al. 2014), while mimicking stand replacing disturbances in other sites is constrained by forest health or direct protective functions of the forest. ...
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What is Closer to Nature Forest Management? Closer-to-Nature Forest Management is a new concept proposed in the EU Forest Strategy for 2030, which aims to improve the conservation values and climate resilience of multifunctional, managed forests in Europe. Building on the latest scientific evidence, this report attempts to define the concept based on a set of seven guiding principles. It also outlines a framework/checklist for flexible European-wide implementationof the concept. The 7 principles of Closer-to-Nature Forest Management are: 1. Retention of habitat trees, special habitats, and dead wood 2. Promoting native tree species as well as site adapted non-native species 3. Promoting natural tree regeneration 4. Partial harvests and promotion of stand structural heterogeneity 5. Promoting tree species mixtures and genetic diversity 6. Avoidance of intensive management operations 7. Supporting landscape heterogeneity and functioning This report analyses the current pressures on forest biodiversity as well as on the health of, and resilience in, managed forests. It examines existing nature-oriented forest management approaches in Europe and analyses their ability to support biodiversity, their stability and adaptability to uncertain future conditions. It proposes a definition, a set of guiding principles and a framework for flexible European-wide implementation of Closer-to-Nature Forest Management. Finally, it evaluates barriers and enablers for implementation and presents a list of existing networks that can be used to assist the dissemination of Closer-to-Nature Forest Management throughout Europe. How can we implement this new concept? 1. Different regions need different management approaches: While the general principles of Closer-to- Nature Forest Management should be similar across all regions, varying but related management approaches should be used in different regions of Europe. This reflects the variation in forest types across the continent, differences in the intensity and scale of natural disturbance regimes, and the ways forests have been used in the past and will have to be managed in the future. 2. Learn from the past and consolidate existing networks and demonstrations: There is a long European tradition of nature-based forest management concepts, and there are many opportunities to learn from existing practices. Because the wider adoption of Closer-to-Nature Forest Management will require a substantial effort in knowledge transfer, it is very important to consolidate existing networks of trials and demonstrations. Such a knowledge transfer network should cover all major regions and forest types found in Europe and could be linked to others seeking to preserve traditional and sustainable management methods, cultural landscapes and their associated biocultural diversity. This will be invaluable in the ongoing social learning process and in helping to convince forest managers and other stakeholders of the benefits of this approach. 3. Use adaptive management as a way to tackle uncertainties: We need to regularly monitor forest responses to management interventions, evaluate these responses and adjust management strategies accordingly. A similar adaptive approach is urgently required to evaluate the impact of policy measures and support mechanisms proposed to encourage adoption of Closer-to-Nature Forest Management. 4. Not a quick-fix, long-term measures are needed: The introduction of Closer-to-Nature Forest Management is not a ‘quick-fix’ and policy makers must provide long-term and consistent support measures to encourage forest managers and other stakeholders to adopt this strategy. Support for forest owners for training and application of the strategy is key. 5. Review existing subsidy and taxation regimes for private owners: Convincing private owners to follow this approach will require the creation of schemes that reward them for providing ecosystem services. Closer-to- Nature Forest Management has the potential to support biodiversity, adapt forests to climate change and provide ecosystem services to a higher level than conventional forest management. There is an urgent need to review existing subsidy and taxation regimes affecting private forestry, and to consider how these might be changed to further the uptake of Closer-to-Nature Forest Management. 6. Develop and use new technologies and tools: There is a need to harmonize monitoring systems and to develop and use new technologies and tools (GIS, GPS and remote sensing) to ease management of these more diverse and structure-rich forests. Finally, there are still some uncertainties about the effect of certain elements of Closer-to-Nature Forest Management on biodiversity conservation and ecosystem health, and how they will affect other ecosystem services including wood production under different management conditions throughout Europe. This calls for more collective learning, experimentation and research.
... The structural variability of primary forests arises largely as a consequence of natural disturbances (Franklin et al., 2002;Franklin and Pelt, 2004;Trotsiuk et al., 2014;Čada et al., 2016Čada et al., , Meigs et al., 2017. Disturbance results in structural reorganization, reduction in living tree densities, increased canopy openness, heterogeneous regeneration of trees and ground vegetation, and increased standing and lying dead wood (Donato et al., 2012). ...
Article
Primary forests are characterized by high vertical and horizontal stand diversity, which provides habitat for a diverse range of species with complex habitat requirements. Detailed knowledge of related ecological processes and habitat development of primary forest species are essential to inform forest management and biodiversity conservation decisions, but relationships are not well documented. We collected dendrochronological data and inventoried numerous structural elements in permanent plots throughout the primary temperate forests within the Carpathian Mountains. We fit and compared multiple predictive models to quantify the importance of 200 years of natural disturbance dynamics on the occurrence probability of an umbrella species – the capercaillie (Tetrao urogallus). We showed that a mixed-severity disturbance regime ranging from low through moderate to high severity disturbances is required to generate diverse forest habitats suitable for capercaillie. The variation in natural disturbance severity and its timing promoted key structural habitat elements, such as low natural regeneration density, low mature tree density, high ground vegetation cover, availability of forest gaps, and abundance of standing deadwood. This study demonstrates the importance of natural disturbance in maintaining the variety of conditions necessary to support primary forest specialist species. Managers of protected areas should be mindful that natural disturbances generate habitat for the capercaillie in mountain Norway spruce forests. Further intervention is unnecessary. Conservation planning and forest reserve design should shift focus to the large-scale spatial requirements needed to ensure that a wide range of forest developmental phases are represented in protected areas.
... Disturbance chronologies have usually been truncated when the sample size drops below 10 (Butler and Sawyer, 2008;Fraver et al., 2009). However, even a lower sample size (7) showed reliable results at the community level (Cada et al., 2016). Samonil et al. (2015) identified the level of uncertainty for such low sample size and suggested following solutions: 1) increase sample size, 2) truncate the starting year of disturbance chronology and/or 3) broadening the merging intervals of disturbance chronology. ...
Article
Disturbances play an important role in forest dynamics. The determination of long-term spatiotemporal characteristics of disturbance regimes is essential for understanding forest dynamics and its shifts under global changes. Tree rings are known to provide detailed insight into both temporal and spatial patterns of forest disturbance history. One of the most commonly used indirect tree-ring techniques for investigating past disturbances is growth release detection (GRD), i.e. the abrupt radial growth increase of trees as a reaction to improved light conditions after the death of a disturbed neighbouring canopy tree or trees. However, there are several issues which have not been addressed so far. Here, an overview of GRD and guide for researchers aiming to incorporate GRD into their research is provided, with focus on conventional running mean methods. The aim is to cover various issues of the GRD procedure such as sampling strategy and data quality, selection of appropriate methods and parameter settings, suggested analysis procedures as well as result presentation. Overall, the importance of GRD incorporation in multidisciplinary studies of forest dynamics is highlighted, as it offers a precise tool for gathering long-term information about past disturbances. Lastly, this paper also suggests several future challenges focused on possible utilization of GRD in mainstream ecology to answer long-standing global ecological questions and improve understanding of past processes in forest ecosystems.
... A substantial proportion of the extant Bohemian forest developed following a period of high natural disturbance activity in the early 1800s. Most stands are considered to be relatively unmodified by anthropogenic land use, as logging rates were limited in the 19th century and increasingly curtailed by conservation measures in the 20th century (Brůna et al., 2013;Č ada et al., 2016;Svoboda et al., 2012). A majority of the region is now protected by two reserves, the Bavarian Forest National Park in Germany and Š umava National Park in Czechia. ...
Article
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Plant traits are an expression of strategic tradeoffs in plant performance that determine variation in allocation of finite resources to alternate physiological functions. Climate factors interact with plant traits to mediate tree survival. This study investigated survival dynamics in Norway spruce (Picea abies) in relation to tree-level morphological traits during a prolonged multi-year outbreak of the bark beetle, Ips typographus, in Central Europe. We acquired datasets describing the trait attributes of individual spruce using remote sensing and field surveys. We used nonlinear regression in a hypothesis-driven framework to quantify survival probability as a function of tree size, crown morphology, intraspecific competition and a growing season water balance. Extant spruce trees that persisted through the outbreak were spatially clustered, suggesting that survival was a non-random process. Larger diameter trees were more susceptible to bark beetles, reflecting either life history tradeoffs or a dynamic interaction between defense capacity and insect aggregation behavior. Competition had a strong negative effect on survival, presumably through resource limitation. Trees with more extensive crowns were buffered against bark beetles, ostensibly by a more robust photosynthetic capability and greater carbon reserves. The outbreak spanned a warming trend and conditions of anomalous aridity. Sustained water limitation during this period amplified the consequences of other factors, rendering even smaller trees vulnerable to colonization by insects. Our results are in agreement with prior research indicating that climate change has the potential to intensify bark beetle activity. However, forest outcomes will depend on complex cross-scale interactions between global climate trends and tree-level trait factors, as well as feedback effects associated with landscape patterns of stand structural diversity.
... Forests that exhibit reverse J-shaped distributions are more structurally complex by having a diversity of tree size and age classes yet such a distribution might not be within the range of natural dynamics of primary spruce forests because they have been historically shaped by mixed-severity disturbances (e.g. Č ada et al., 2016;Meigs et al., 2017). ...
Article
Natural disturbances strongly influence forest structural dynamics, and subsequently stand structural heterogeneity, biomass, and forest functioning. The impact of disturbance legacies on current forest structure can greatly influence how we interpret drivers of forest dynamics. However, without clear insight into forest history, many studies default to coarse assumptions about forest structure, for example, whether forests are even or unevenly aged. The aim of this study was to analyze the effects of past disturbances on the current diameter distributions of Norway spruce (Picea abies (L.) Karst.)-dominated landscapes throughout the Carpathian Mountains. Our dendroecological dataset comprises tree cores from 339 plots (7,845 total tree cores), nested within 28 primary forest stands, known to vary greatly in the severity of historical disturbances. Our analyses revealed that historical disturbances had a strong and significant effect on the current diameter distribution shapes at the plot level. We demonstrated that mixed-severity disturbance regimes were more frequent and create a complex pattern of diameter distributions at the plot and stand scale. Here, we show that high severity disturbance was associated with unimodal diameter distributions, while low and moderate severity was associated with the reverse J-shaped distribution. This is a result of complex disturbance patterns, with structural biological legacies. Our results will have important management implication in the context of tree size heterogeneity, biomass storage, and productivity as influenced by natural disturbances. Lastly, these results demonstrate that structural changes may arise as consequences of changing disturbance regime associated with global change.
... Spruce stands have been dying out since the end of the 1950s. The dying-off process in mountain spruce forests was caused by several biotic (bark beetles) and non-biotic factors (air pollution), forming a cause-and-effect chain that reinforced the disease process, resulting in a total annihilation of the stand over an extended period of time [81][82][83]. Air pollution, prolonged summer droughts in the years 2003-04 and 2006-07, and the catastrophic hurricane of 2004 resulted in the weakening of spruce stands in the montane zone [84,85]. ...
Article
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Changes in forest range are caused by human activity in many regions of the world. The aim of this paper is an attempt to determine the impact of pastoral and forest management on changes in forest cover and their fragmentation in the Silesian Beskids (southern Poland) in 1848–2015. Historical maps and landscape metrics were used to study changes in forest cover. Using a digital map of forests, analyses of the distribution of forest communities, site types and their condition were conducted. Since 1848 the forest area has increased by 11.8%, while the area of forest core zones has increased by 16.2%, accompanied by a 4.5% reduction in the forest’s internal bu�er zone. From the mid-nineteenth century, the forest range has been systematically growing from 82.1 to 93.9% because of the pastureland abandonment and forest regeneration, despite temporary logging resulting in forest fragmentation. Minor changes in core area index (CAI) from 80.41 to 87.55 indicate that pastoral economy did not result in considerable fragmentation of forests. The impact of forest management was greater as the sites characterised by natural condition occupy only 28% of the forest land and anthropogenically transformed ones dominate occupying over 50%. An artificial spruce monoculture was died-o� and large felling areas were created at the beginning of the twenty-first century covering almost 40% of the study area.
... Disturbances caused by natural factors have occurred in the past and cannot be avoided in the future. In the years 1950-2000, the annual average timber volume damaged by disturbances was 35 million m 3 [14][15][16]. ...
Article
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The area of forests and the standing volume per hectare are constantly increasing in Eu-rope, and this trend is expected to continue for several more decades; the aim of this paper was to provide an empirical overview of the development of disturbances in selected countries of central Europe and based on this overview to empirically model and predict the development and intensity of disturbances in the future. Statistical methods (Holt-Winters) and predictive risk models of the growth simulator SIBYLA were used for prediction. From the statistically predicted values by this method, it follows that, in the next three years, it is possible to assume that stagnation will result in declining volumes of incidental fellings in all countries. Forecast from the growth simulator SIBYLA shows a substantial increase in the predicted volume of incidental fellings for the years 2021 and 2022, compared with 2020. The volumes of incidental fellings should grow most significantly, especially in Germany, Poland, and Austria. The performed analysis and predictions suggest that the peak of wood volumes damaged by disturbances in the next decade will probably be reached already in the reports for 2021 or 2022. However, the risk of disturbances remains high, and other large-scale area disturbances in forest ecosystems cannot be completely ruled out.
... More large, high severity disturbances may cause a homogenization of forests, amplifying future climate impacts and potentially leading to forest loss . Increases in the frequency of low to moderate severity disturbances (e.g., small-scale windthrow, or insect outbreaks in mixed forests), however, may enhance structural and compositional complexity (Čada et al., 2016;Halpin & Lorimer, 2016) and dampen the effect of future climate-mediated disturbances (Sommerfeld et al., 2021). More broadly, a development towards structurally and functionally complex forests (e.g., found in old-growth forests) is expected to buffer the effects of climate change compared with younger and/ or less complex forests (Bauhus et al., 2009;. ...
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Observational evidence suggests that forests in the Northern Alps are changing at an increasing rate as a consequence of climate change. Yet, it remains unclear whether the acceleration of forest change will continue in the future, or whether downregulating feedbacks will eventually decouple forest dynamics from climate change. Here we studied future forest dynamics at Berchtesgaden National Park, Germany by means of a process‐based forest landscape model, simulating an ensemble of 22 climate projections until the end of the 21st century. Our objectives were (i) to assess whether the observed acceleration of forest dynamics will continue in the future, (ii) to analyze how uncertainty in future climate translates to variation in future forest disturbance, structure, and composition, and (iii) to determine the main drivers of future forest dynamics. We found that forest dynamics continue to accelerate in the coming decades, with a trend towards denser, structurally more complex and more species rich forests. However, changes in forest structure leveled off in the second half of the 21st century regardless of climate scenario. In contrast, climate scenarios caused trajectories of tree species change to diverge in the second half of the 21st century, with stabilization under RCP 2.6 and RCP 4.5 scenarios and accelerated loss of conifers under RCP 8.5. Disturbance projections were 3 to 20 times more variable than future climate, whereas projected future forest structure and composition varied considerably less than climate. Indirect effects of climate change via alterations of the disturbance regime had a stronger impact on future forest dynamics than direct effects. Our findings suggest that dampening feedbacks within forest dynamics will decelerate forest change in the second half of the 21st century. However, warming beyond the levels projected under RCP 4.5 might profoundly alter future forest disturbance and composition, challenging conservation efforts and ecosystem service supply.
... We simulated three disturbance scenarios: historic disturbance, future disturbance and no disturbance. The three scenarios differed in disturbance frequency, as determined by the disturbance rotation period (i.e. the average time it takes for the cumulative area of disturbance to reach the size of the study landscape), which was set to 400 years in the historic disturbance scenario (Čada et al., 2016;Thom et al., 2013), and to 200 years in the future disturbance scenario . This implies that in the future disturbance scenario twice as many disturbance events occurred compared to the historic disturbance scenario, which is within the range of expec- In total, 5,040 simulation runs with a duration of 200 years were conducted (2 models × 2 landscapes × [3 levels of gamma diversity × 2 spatial configurations +1 × no diversity] × 3 climate scenarios × 3 disturbance scenarios × 20 replicates). ...
Article
Single species forest systems often suffer from low resistance and resilience to perturbations. Consequently, fostering tree species diversity is discussed as an important management approach to address the impacts of changing climate and disturbance regimes. Yet, the effect of the spatial grain of tree species mixtures remains unknown. We asked whether increasing tree species diversity between stands (beta diversity) has the same effect as increasing tree species diversity within stands (alpha diversity) at similar overall levels of richness (gamma diversity). We conducted a multi‐model simulation experiment under climate change, applying two forest landscape models (iLand, LandClim) across two contrasting landscapes of Central Europe. We analyzed the effect of different levels and configurations of diversity on the disturbance impact and the temporal stability of biomass stocks and forest structure. In general, increasing levels of diversity decreased disturbance impacts. Positive diversity effects increased with increasing severity of climate change. Beta diversity buffered disturbance impacts on landscape‐level biomass stocks more strongly than alpha diversity. The effects of the spatial configuration on forest structure were more variable. Diversity effects on temporal stability were less pronounced compared to disturbance impacts, and mixture within and between stands had comparable effects on temporal stability. Diversity effects were context‐dependent, with patterns varying between landscapes and indicators. Furthermore, we found a strong species identity effect, with increasing diversity being particularly beneficial in conifer‐dominated systems of the European Alps. The two models agreed on the effects of different levels and configurations of tree species diversity, underlining the robustness of our findings. Synthesis and application: Enhancing tree species diversity can buffer forest ecosystems against increasing levels of perturbation. Mixing tree species between stands is at least as effective as mixing tree species within stands. Given the managerial advantages of between‐stand mixtures (e.g., reduced need to control competition in order to maintain diversity, higher timber quality, lower logistic effort), we conclude that forest management should consider enhancing diversity at multiple spatial scales.
... Furthermore, natural or human disturbances including wind, tree mortality and harvesting, create heterogeneity in forest structure (e.g. gaps) (Nakashizuka and Matsumoto, 2002;Čada et al., 2016), which further modify the characteristics of understorey solar irradiance. Solar irradiance modulates litter decomposition processes through photodegradation, which mainly consists of direct photomineralization and indirect photofacilitation (Gallo et al., 2009;King et al., 2012;Almagro et al., 2015;Liu et al., 2018). ...
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Decomposition of plant organic matter plays a key role in the terrestrial biogeochemical cycles. Sunlight has recently been identified as an important contributor to carbon [C] turnover through photodegradation, accelerating decomposition even in forest ecosystems where understorey solar irradiance remains relatively low. However, it is uncertain how C and nutrients dynamics respond to fluctuations in solar spectral irradiance caused by canopy structure (understorey vs. gaps) and season (open vs. closed canopy phenology). Spectral-attenuation treatments were used to compare litter decomposition over eight months, covering canopy phenology, in a temperate deciduous forest and an adjacent gap. Exposure to the full spectrum of sunlight increased the loss of litter C and lignin by 75% and 64% in the forest gap, and blue light was responsible for respectively 27% and 42% of that loss. Whereas in the understorey, C and lignin loss were similar among spectral-attenuation treatments over the experimental period, except prior to and during spring canopy flush when exposure to the full spectrum of sunlight promoted C loss by 15% overall, 80% of which was attributable to ultraviolet-B (UV-B) radiation. Nitrogen [N] was immobilized in the understorey during canopy flush before the canopy completely closed but N was swiftly released during canopy leaf-fall. Our study suggests that blue-driven photodegradation plays an important role in lignin decomposition and N dynamics in canopy gaps, whereas seasonal canopy phenology affecting sunlight reaching the forest floor drastically changes patterns of C and N in litter during decomposition. Hence, including sunlight dynamics driven by canopy structure and phenology would improve estimates of biogeochemical cycling in forests responding to changes in climate and land-use.
... Natural disturbances are widely acknowledged to be a primary force in the dynamics of diverse primeval forest ecosystems, shaping the forest structure and composition and maintaining species and soil diversity [1][2][3][4][5][6]. Whereas fine-scale disturbances dominate the natural forest dynamics of deciduous upland forests of Central Europe [7][8][9][10], several studies have highlighted the importance of large-scale, stand-replacing events for conifer mountain forest ecosystems [11][12][13][14][15]. More recently, a mixed-severity disturbance regime, predominantly driven by gap dynamics with infrequent severe stand-replacing events, has been documented for some mixed mountain forest ecosystems [8,13,[16][17][18][19][20]. ...
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The driving forces of tree mortality following wind disturbances of mountain mixed European temperate forests belongs among issues not comprehensively resolved. Hence, we aimed to elucidate the key factors of tree resistance to historical severe disturbance events in the Boubínský Primeval Forest, one of the oldest forest reserves in the Czech Republic. By using spatially explicit tree census, dendrochronological and soil data, we study spatial and temporal patterns of past disturbances and mathematically compared selected characteristics of neighboring trees that were killed by a severe storm in 2017 and those that remained undisturbed. The tendency of trees toward falling was primarily driven edaphically, limiting severe events non-randomly to previously disturbed sites occupied by hydromorphic soils and promoting the existence of two spatially-separated disturbance regimes. While disturbed trees usually recruited in gaps and experienced only one severe release event, surviving trees characteristically regenerated under the canopy and were repeatedly released. Despite the fact that disturbed trees tended to reach both lower ages and dimensions than survivors, they experienced significantly higher growth rates. Our study indicates that slow growth with several suppression periods emerged as the most effective tree strategy for withstanding severe windstorms, dying of senescence in overaged life stage. Despite the selective impact of the Herwart storm on conifer population, we did not find any difference in species sensitivity for most characteristics studied. We conclude that the presence of such ancient, high-density wood trees contributes significantly to the resistance of an entire stand to severe storms.
... In the Tatras, similar calamities of a smaller extent occurred, for example, in the early 20th century. Those areas influenced by stand replacing disturbances will be resistant to further disturbances for several decades, because of the more resilient forest structure (bark beetle usually attacks trees older than 60 years, when considering natural conditions) [5,6]. However, more frequent bark beetle outbreaks are expected in the future, as a consequence of climate change [41]. ...
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High winds and the subsequent infestation of subcortical insect are considered to be the most extensive types of large natural disturbances in the Central European forests. In this paper, we focus on the landscape dynamics of two representative mountain areas of Slovakia, which have been affected by aforementioned natural disturbances during last two decades. For example, on 19 November 2004, the bora caused significant damage to more than 126 km2 of spruce forests in the Tatra National Park (TANAP). Several wind-related events also affected sites in the National Park Low Tatras (NAPALT). Monitoring of related land cover changes during years 2000–2019 was based on CORINE Land Cover data and methodology set up on satellite and aerial images interpretation, on detailed land cover interpretation (1:10,000) for the local case studies, as well as on the results of field research and forestry databases. The dynamics of forest recovery are different in the clear-cuts (usually with subsequent tree planting) and in the naturally developing forest. The area in the vicinity of Tatranská Lonmnica encroaching on the Studená dolina National Nature Reserve in TANAP represents a trend of the gradual return of young forest. The area of Čertovica on the border between NAPALT and its buffer zone are characterized by an increase in clear-cut sites with potentially increasing soil erosion risk, due to repeated wind disasters and widening of bark beetle. Proposed detailed, large-scale approach is being barely used, when considering recent studies dealing with the natural disturbances.
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Disentangling the long-term changes in forest disturbance dynamics provides a basis for predicting the forest responses to changing environmental conditions. The combination of multidisciplinary records can offer more robust reconstructions of past forest disturbance dynamics. Here we link disturbance histories of the central European mountain spruce forest obtained from dendrochronological and palaeoecological records (fossil pollen, sedimentary charcoal, bark beetle remains and geochemistry) using a small glacial lake and the surrounding forest in the Šumava National Park (Czech Republic). Dendrochronological reconstructions of disturbance were created for 300-year-long records from 6 study plots with a minimum of 35 trees analyzed for the abrupt growth increases (releases) and rapid early growth rates, both indicative of disturbance events. High-resolution analysis of lake sediments were used to reconstruct 800-year long changes in forest composition and landscape openness (fossil pollen), past fire events (micro- and macroscopic charcoal), bark beetle occurrence (fossil bark beetle remains), and erosion episodes (geochemical signals in the sediment) potentially resulting from disturbance events. Tree-ring data indicate that disturbances occurred regularly through the last three centuries and identify a most intensive period of disturbances between 1780 and 1830 CE. Geochemical erosion markers (e.g. K, Zr, % inorganic) show greater flux of catchment sediment and soils in the periods 1250–1400 and 1450–1500 CE, before a substantial shift to a more erosive regime 1600–1850 and 1900 CE onwards. Pollen records demonstrate relatively small changes in forest composition during the last 800 years until the beginning of the 20th century, when there was decrease in Picea. Fossil bark beetle remains indicate continuous presence of bark beetles from 1620s to 1800s, and charcoal records suggest that more frequent fires occurred during the 18th century. Each of the dendrochronological, palaeoecological and sedimentological records provide a unique perspective on forest disturbance dynamics, and combined offer a more robust and complete record of disturbance history. We demonstrate that sedimentary proxies originating from the lake catchment mirror the forest disturbance dynamics recorded in the tree-rings. The multidisciplinary records likely record forest disturbances at different spatial and temporal scales revealing different disturbance characteristics. Integrating these multidisciplinary datasets demonstrates a promising way to obtain more complete understanding of long-term disturbance dynamics. However, integrating datasets with variable spatial and temporal influence remains challenging. Our results indicated that multiple disturbance factors, such as windstorms, bark beetle outbeaks and fires, may occur simultaneously creating a complex disturbance regime in mountain forests, which should be considered in forest management and conservation strategies.
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Natural subalpine forests are considered to be sensitive to climate change, and forest characteristics are assumed to reflect the prevalent disturbance regime. We hypothesize that stand history determines different stand structures. Based on large full inventory datasets (including tree biometric data, spatial coordinates, tree age, and basal area increment) we assessed the size structure, tree recruitment dynamics and radial growth patterns in three permanent plots along an altitudinal gradient in a mixed coniferous forest (Picea abies and Pinus cembra) in the Eastern Carpathians. Both discrete disturbances (large scale or small scale) and chronic disturbances (climate change) were identified as drivers of stand structure development in the studied plots. A stand replacing wind disturbance generated a unimodal bell-shaped size and age distribution for both species characterized by a sharp increase in post-disturbance recruitment. By contrast, small-scale wind-caused gaps led to a negative exponential diameter distribution for spruce and a left-asymmetric unimodal for pine. Climate-driven infilling processes in the upper subalpine forest were reflected as J-shaped size and age distributions for both species, but with pine predating spruce. The growth patterns for both species demonstrated an increased basal area increment since the early 1900s, with an emphasis in the last few decades, irrespective of stand history. Pine demonstrated a competitive advantage compared to spruce due to the higher growth rate and size at the same age. Recognition of combined discrete and chronic disturbances as drivers of the tree layer characteristics in a subalpine coniferous forest is essential in both stand history analyses and growth predictions.
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European natural mountain Norway spruce (Picea abies) forests are currently subject to extensive disturbances. An improved understanding of the self-regulated regenerative capacity of this forest type is therefore needed. We used the last remnant of natural mountain Norway spruce forests in central northwestern Europe (BNF Brocken natural forest), to analyze (1) the diversity of structure and age distribution of the tree population and (2) the effect of disturbances on self-regulated tree regeneration over the last 264 years. To this end, we combined an assessment of stand structure with dendrochronological investigations and a review of disturbance history. We hypothesized that BNF exhibits a high diversity of tree ages and dimensions and that recruitment and survival of tree regeneration were largely independent from disturbances. BNF showed a high structural and age diversity. Disturbances exhibited no regular temporal pattern. Their effect on tree regeneration was rather complex and changed with observation period. Impeding and facilitating effects of past disturbances on recruitment were significant from 1736 to 1910. From 1911 until 2000, recruitment decoupled from preceding disturbances. Subsequent disturbances facilitated survival of established trees from 1736 to 1820, while afterward no significant influence could be proved. Our study showed that in the course of self-regulated development the tree population of BNF has gradually acquired, or maintained, a diverse structure. Disturbances served as an important driver of diversification. We concluded that increasing deadwood availability and limiting browsing are the key to securing immediate regeneration.
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Investigating the disturbance regimes of unharvested forests helps us understand their past, present, and future trajectory and gives us a model for forest management. It can also clarify the relative importance of small-scale gap dynamics versus more severe disturbances. Here we used tree rings to examine the recruitment patterns, growth dynamics, and disturbance chronologies of American beech (Fagus grandifolia), sugar maple (Acer saccharum), and eastern hemlock (Tsuga canadensis) in A.B. Williams Woods, an old-growth forest in Ohio, USA, over the past 250 years. We found that beech and sugar maple recruitment peaked around 1900 and continued through the 1900s, while hemlock recruitment peaked during 1825–1875, then declined and effectively ended in the early 1900s. Hemlock grew fastest during the 1800s according to ring width and basal area increment, while sugar maple ring width surpassed beech and hemlock in the 1900s. All three species showed a dramatic increase in growth from 1980 to 2010. Beech and sugar maple established regardless of canopy gaps, but 73% of hemlocks originated in gaps. In most decades, <10% of trees experienced gap recruitment or growth release, suggesting that ongoing, endogenous canopy mortality was the primary disturbance shaping this forest. However, a more severe forest-wide disturbance occurred during the 1980s–1990s when the scale insect causing beech bark disease was introduced, with greater than 30% of living trees showing growth releases in those decades. Another synchronous release occurred in the 1930s when blight-killed chestnuts were removed; 16% of trees showed releases. Both of these intermediate-severity disturbances involved human introduction of invasive species. Thus, we documented a natural disturbance regime of small-scale gap dynamics, punctuated by more severe anthropogenic disturbances in the twentieth century. These relatively frequent, intermediate-severity events probably mean that the forest’s current composition is non-equilibrial. Hemlock may continue to decline while beech maintains its dominance by constant regeneration in both gaps and shade, and by responding to disturbance with root suckering and growth pulses. The codominance of sugar maple may be relatively recent, and perhaps temporary, as we found little sugar maple recruitment before 1875 or after 1950, and three times fewer sugar maple saplings now than in the early 1900s. Despite being protected as a park, the development of this old-growth forest has been shaped more by disease-causing invasive species than natural disturbances over the past century. This result emphasizes the pervasiveness of human impacts even in communities we look to as examples of natural pattern and process.
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In 1927, the first pollen diagram was published from the Bohemian/Bavarian Forest region of Central Europe, providing one of the first qualitative views of the long-term vegetation development in the region. Since then significant methodological advances in quantitative approaches such as pollen influx and pollen-based vegetation models (e.g., Landscape Reconstruction Algorithm, LRA) have contributed to enhance our understanding of temporal and spatial ecology. These types of quantitative reconstructions are fundamental for conservation and restoration ecology because they provide long-term perspectives on ecosystem functioning. In the Bohemian/Bavarian Forests, forest managers have a goal to restore the original forest composition at mid-elevation forests, yet they rely on natural potential vegetation maps that do not take into account long-term vegetation dynamics. Here we reconstruct the Holocene history of forest composition and discuss the implications the LRA has for regional forest management and conservation. Two newly analyzed pollen records from Prášilské jezero and Rachelsee were compared to 10 regional peat bogs/mires and two other regional lakes to reconstruct total land-cover abundance at both the regional-and local-scales. The results demonstrate that spruce has been the dominant canopy cover across the region for the past 9,000 years at both high-(>900 m) and mid-elevations (>700-900 m). At the regional-scale inferred from lake records, spruce has comprised an average of ∼50% of the total forest canopy; whereas at the more local-scale at mid-elevations, spruce formed ∼59%. Beech established ∼6,000 cal. years BP while fir established later around 5,500 cal. years BP. Beech and fir growing at mid-elevations reached a maximum land-cover abundance of 24% and 13% roughly 1,000 years ago. Over the past 500 years spruce has comprised ∼47% land-cover, while beech and fir comprised ∼8% and <5% at mid-elevations. This approach argues for the "natural" development of spruce and fir locally in zones where the paleoecology indicates the Carter et al. Quantitative Palynology and Conservation Management persistence of these species for millennia. Contrasting local and regional reconstructions of forest canopy cover points to a patchwork mosaic with local variability in the dominant taxa. Incorporation of paleoecological data in dialogues about biodiversity and ecosystem management is an approach that has wider utility.
Chapter
Outbreaks of the eruptive Eurasian spruce bark beetle (Ips typographus) have led to extensive mortality of European Norway spruce (Picea abies) forests causing severe economic losses, but also initiating forest succession and regeneration. Establishment and reproduction of I. typographus and its assemblage of microbial partners is initiated by pheromone-mediated mass attacks to circumvent the host's formidable chemical and anatomical defenses. However, in contrast to its host tree, which is poorly adapted to climatic conditions outside its natural habitat, I. typographus benefits from a warm and dry environment. Increasing temperatures promote multivoltine bark beetle populations; yet, their consequences for hibernation and diapause are still unclear. Existing knowledge of I. typographus has focused on individual aspects of the bark beetle development and host defense. To gain an improved understanding of climate-driven ecological changes in forest ecosystems, the complex interplay between climate change, beetle phenology, associated microbes, and tree physiology should be studied under natural field and laboratory conditions.
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Forest ecosystems worldwide are subjected to human-induced stressors, including eutrophication and acidification, and to natural disturbances (for example, insect infestation, windstorms, fires). The occurrence of the later is expected to increase due to the ongoing climate change. These multi-stressor forcings modify ecosystem biogeochemistry, including the retention of limiting nutrients, with implications for terrestrial and aquatic biodiversity. Here we present whole ecosystem nutrient (N, Ca, Mg, K) mass balances in the forested catchment of Plešné Lake, CZ, which has undergone transient changes linked to the recovery from anthropogenic acidification and to the forest disturbances caused by severe infestations by the bark beetle (Ips typographus). Measured fluxes and storage of nutrients in the lake-catchment ecosystem were used to constrain the process-oriented biogeochemical model MAGIC (Model of Acidification of Groundwater In Catchments). Simulated lake water chemistry and changes in soil nutrient pools fitted observed data and revealed that (1) the ecosystem N retention declined, thus nitrate leaching increased for 10 years following the bark beetle disturbance, with transient adverse effects on the acid–base status of lake water, (2) the kinetics of nutrient mineralisation from decaying biomass coupled with nutrient immobilisation in regrowing vegetation constrained the magnitude and duration of ecosystem losses of N, Ca and Mg, (3) the excess of mineralised base cations from decomposing biomass replenished the soil cation exchange matrix, which led to increased soil base saturation, and (4) the improvement of the catchment soil acid–base status led to an increase of lake water pH and acid neutralising capacity. Forested ecosystems underlain by nutrient-poor soils and bedrock are prone to human-induced damages caused by acidification and eutrophication, and any natural disturbance may further lead to nutrient imbalances. We demonstrated that in this natural forest ecosystem protected from human intervention, disturbances together with natural post-disturbance vegetation recovery have temporally positive effects on the nutrient stores in the soil.
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The Bohemian Forest lakes, situated along the Czech-German-Austrian border, were strongly affected by atmospheric acidification between the 1950s and the late 1980s. The subsequent chemical recovery of the lake water should precede and enable a biological recovery, including changes in caddisfly (Insecta: Trichoptera) assemblages. Nevertheless, local pre-acidification data and detailed knowledge of the lake district history are missing, making evaluation of lake recovery difficult. We performed high-resolution analysis of caddisfly remains in a 2.2 m long sediment profile from Prášilské Lake covering the complete history of the lake-catchment evolution. Caddisfly larvae are good indicators of environmental conditions and their subfossil remains are well preserved in unconsolidated waterlaid sediments. A total of 10 caddisfly morpho-taxa were found providing a record from 11,400 cal. yr. BP to the present. With the exception of Athripsodes aterrimus, all identified species are currently present in the Bohemian Forest glacial lakes or their inflow streams but not all of them are documented in Prášilské Lake. The caddisfly fauna consisted of acid-resistant, acid-tolerant and eurytopic species since the Early Holocene. Based on our results, the acid, dystrophic state of Prášilské Lake has been occurring since the lake formation. We conclude that the first signs of natural acidification appeared not later than during the Holocene onset in the Bohemian Forest region. Furthermore, we did not detect any abrupt changes in the species composition connected to the period of anthropogenic acidification during the twentieth century. This study provides for the first time a record of postglacial succession of caddisfly assemblages in a central European mountain lake.
Technical Report
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Europe’s forests have provided human societies with essential ecosystem services and great economic values for centuries. Some of these values are now increasingly threatened by climate change, which greatly intensifies forest disturbances such as bark beetle outbreaks. However, some past management practices have also increased the vulnerability of Europe’s forests. For example, due to its good growth performance and favourable properties for forest industry, Norway spruce has been planted extensively in Europe over the past century, including in areas outside its native range. This has created large areas of so-called secondary forests, which have increasingly exhibited problems with health and vitality and are prone to various disturbances: the most important being wind, drought and bark beetles. This report aims to help European and national policy makers understand the complex roles bark beetles play in our forests, and provide the scientific basis for robust forest policies and management options to address these emerging bark beetle problems.
Technical Report
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Evropské lesy poskytovaly lidské společnosti po staletí mnohé ekosystémové služby a generovaly značné ekonomické hodnoty. Některé z těchto benefitů jsou stále více ohrožovány změnou klimatu, která znásobuje vliv různých disturbančních činitelů, jako jsou např. kůrovci. Zranitelnost evropských lesů nepříznivě ovlivnil i jejich dlouhodobý management. Například smrk ztepilý byl pro svůj rychlý růst a příznivé technické vlastnosti v minulých stoletích hojně vysazován mimo areál svého přirozeného rozšíření. Tím vznikly rozsáhlé plochy tzv. sekundárních smrkových lesů, které měly stále větší problémy se zdravotním stavem a vitalitou, a byly náchylné k poškození činiteli, jako je vítr, sucho a kůrovec. Tato studie má za cíl pomoci při tvorbě evropských a národních lesnických strategií, přispět k lepšímu pochopení působení kůrovce na lesy, a poskytnout vědecká východiska pro lesnické strategie umožňující zvládat současné kůrovcové kalamity.
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Stürme erzeugen je nach Windstärke und Windfeld kleine bis großflächige Störungen, wovon Wälder wegen ihrer Höhe und Ausdehnung am stärksten betroffen sind. In West-, Mittel- und Nordeuropa ereignen sich in Bezug auf das betroffene Holzvolumen die größten Sturmschäden, zudem stellt Wind den bedeutendsten Störfaktor für Wälder dar. Fichten sind in Mitteleuropa anfälliger gegenüber Winterstürmen als winterkahle Bäume. Stammbruch und Entwurzelung hängen auch von artspezifischen, standörtlichen und bestandsstrukturellen Faktoren ab. Bäume passen sich durch Bildung von Druckholz an wiederkehrende Windbeanspruchung an. Windwurfflächen bewalden sich in Tieflagen rascher als in Hochlagen. In naturbelassenen und geräumten Störungsflächen verjüngt sich der Wald ähnlich rasch. Mit dem Klimawandel dürften Waldschäden durch Winterstürme zunehmen.
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Natural or anthropogenic disturbances in the forest ecosystem alter ecological conditions and lead to shifts in microbial diversity. We focused on the topsoil properties of specific sites in Tatra National Park (Slovakia) that were affected by windthrow, wildfire and wood extraction. We analyzed soil organic matter content (SOM), dry weight (DW), enzymatic activity including dehydrogenase activity (DHA), fluorescein diacetate hydrolysis (FDH) and phosphomonoesterase (PME). Bacterial community profiles were analyzed using the PCR-DGGE approach, and Ellenberg’s indicator values (EIV) were used as eco-indices of studied sites. Dystric Cambisol was sampled at sites distinguished by management approaches established after windthrow in 2004 and wildfire in 2005. We focused on the windthrow site where wooden debris was extracted (EXT); the site left for self-recovery with no intervention (NEX); the site affected by wildfire (FIR), a former reference site damaged by the windstorm in 2014 followed by the extraction of wooden debris (REX), and a non-affected reference spruce stand (REF). The windthrow sites with different management (EXT, NEX) showed relative similarities based on enzymatic activity, bacterial community profiling (85%) and EIV comparison. The FIR site exhibited no similarities (0%) with EXT and NEX in the bacterial community structure. The SOM content correlated only with PME (r² = 0.42) and soil moisture (r² = 0.64). Based on RDA analysis, certain EIVs seem to be suitable indicators of selected soil properties. The lack of differences between NEX and EXT could be caused by the diminishing of post-disturbance effects on microbial communities. The effect of wildfire on microbial activity and bacterial community structure seems to be longer than different management approach.
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Natural spruce forests are restricted to the highest mountain ranges in the Czech Republic. Spruce is also the commonest tree species in managed forests. Owing to a massive decline of spruce forests in Central Europe, caused by recent climatic fluctuations and disturbances, the lichen diversity and species composition was compared between ten representative natural mountain old-growth forests in the Czech Republic and their counterparts in mature managed forests. The old-growth forests are characterized by a higher species richness, abundance, number of Red-listed species, functional, taxonomic and phylogenetic diversities. Plots with the highest species richness are situated in the Šumava Mountains, an area with a relatively low sulphur deposition in the past. Bioindication analysis searching for lichen indicators supported several species (e.g. Xylographa vitiligo, Chaenotheca sphaerocephala) and genera (e.g. Calicium, Xylographa) with a strong preference for old-growth forests. Analysis of lichen functional traits revealed a higher abundance of species with a vegetative reproduction in managed forests that may be explained by a higher efficiency in colonization by young successional stages. Lichens with stalked apothecia, pigmented ascospores and large ascospores are more frequent in old-growth forests. Our results are briefly discussed in terms of nature conservation, focusing on national refugees of old-growth forest species, biodiversity hot-spots, practical use of indicator species and representative measures for an evaluation of forest quality.
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The availability of global digital elevation models (DEMs) from multiple time points allows their combination for analysing vegetation changes. The combination of models (e.g., SRTM and TanDEM-X) can contain errors, which can, due to their synergistic effects, yield incorrect results. We used a high-resolution LiDAR-derived digital surface model (DSM) to evaluate the accuracy of canopy height estimates of the aforementioned global DEMs. In addition, we subtracted SRTM and TanDEM-X data at 90 and 30 m resolutions, respectively, to detect deforestation caused by bark beetle disturbance and evaluated the associations of their difference with terrain characteristics. The study areas covered three Central European mountain ranges and their surrounding areas: Bohemian Forest, Erzgebirge, and Giant Mountains. We found that vertical bias of SRTM and TanDEM-X, relative to the canopy height, is similar with negative values of up to −2.5 m and LE90s below 7.8 m in non-forest areas. In forests, the vertical bias of SRTM and TanDEM-X ranged from −0.5 to 4.1 m and LE90s from 7.2 to 11.0 m, respectively. The height differences between SRTM and TanDEM-X show moderate dependence on the slope and its orientation. LE90s for TDX-SRTM differences tended to be smaller for east-facing than for west-facing slopes, and varied, with aspect, by up to 1.5 m in non-forest areas and 3 m in forests, respectively. Finally, subtracting SRTM and NASA DEMs from TanDEM-X and Copernicus DEMs, respectively, successfully identified large areas of deforestation caused by hurricane Kyril in 2007 and a subsequent bark beetle disturbance in the Bohemian Forest. However, local errors in TanDEM-X, associated mainly with forest-covered west-facing slopes, resulted in erroneous identification of deforestation. Therefore, caution is needed when combining SRTM and TanDEM-X data in multitemporal studies in a mountain environment. Still, we can conclude that SRTM and TanDEM-X data represent suitable near global sources for the identification of deforestation in the period between the time points of their acquisition.
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The disturbance regime of mountain spruce–beech temperate forests has not yet been sufficiently elucidated. We hypothesized that spruce and beech express completely different disturbance histories and behavioural strategies, potentially causing exceptionally complex disturbance regimes. We further hypothesized that the spontaneous development of mountain forests can temporarily result in a simplification of the forest's spatial structure. We wanted to discover how the disturbance history and growth plasticity of the main tree species differ, and whether some old managed forests arose from primeval forest remnants. We compared dendrochronological records of the unmanaged Boubín Primeval Forest and 30 sites with current forestry records. Using this comparison, we categorized all sites into three categories. In the disturbance history of all evaluated forest sites, there was clear evidence of the presence of severe disturbances in the nineteenth century. However, the regeneration of beech was more continuous and less dependent on the presence of severe disturbances than the regeneration of spruce, which depended on the presence of severe disturbances of low frequency. Human-induced changes at some sites were manifested in changes in the initial growth of both species and disrupted their mutual competition and also led to a higher growth plasticity of beech. Despite human impacts in the region since the end of the nineteenth century, about 30% of analysed trees were older than the severe disturbances in the nineteenth century; therefore, some studies sites preserved the characteristics of primeval forest. Our results revealed three main forest development trajectories since the end of the nineteenth century.
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Outbreaks of conifer bark beetles in Europe and North America have increased in scale and severity in recent decades. In this study, we identify existing fossil records containing bark beetle remains from the end of the Last Glacial Maximum (~14,000 cal. yr BP) to present day using the online databases Neotoma and BugsCEP and literature searches, and compare these data with modern distribution data of selected tree-killing species. Modern-day observational data from the Global Biodiversity Information Facility (GBIF) database was used to map recorded distributions from AD 1750 to present day. A total of 53 fossil sites containing bark beetle remains, from both geological and archeological sites, were found during our searches. Fossil sites were fewer in Europe ( n = 21) than North America ( n = 32). In Europe, 29% of the samples in which remains were found were younger than 1000 cal. yr BP, while in North America, remains were mainly identified from late Glacial (~14,000–11,500 cal. yr BP) sites. In total, the fossil records contained only 8 of 20 species we consider important tree-killing bark beetles in Europe and North America based on their impacts during the last 100 years. In Europe, Ips sexdentatus was absent from the fossil record. In North America, Dendroctonus adjunctus, Dendroctonus frontalis, Dendroctonus jeffreyi, Dendroctonus pseudotsugae, Dryocoetes confusus, Ips calligraphus, Ips confusus, Ips grandicollis, Ips lecontei, Ips paraconfusus, and Scolytus ventralis were absent. Overall, preserved remains of tree-killing bark beetles are rare in the fossil record. However, by retrieving bulk material from new and existing sites and combining data from identified bark beetle remains with pollen, charcoal, tree rings, and geochemistry, the occurrence and dominance of bark beetles, their outbreaks, and other disturbance events can be reconstructed.
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Zusammenfassung Bergmischwälder aus Fichte (Picea abies (L.) Karst), Weißtanne (Abies alba Mill.) und Europäischer Rot-buche (Fagus sylvatica) bedecken in Europa eine Gesamtfläche von mehreren Millionen Hektar. Sie verbinden die Buchenwaldgesellschaften im Tiefland mit den fichtendominierten, alpinen Waldtypen. Aufgrund ihrer Höhenzonierung sind diese Wälder besonders von den Auswirkungen des Klimawandels betroffen. Darüber hinaus ermöglichen neue Erschließungstechniken innovative Möglichkeiten einer intensivierten Bergwaldbewirtschaftung. Da jedoch wenig über die langfristige Entwicklung der Produk-tivität dieser Waldsysteme in Europa bekannt ist, sind belastbare Informationen über Produktivität und Anpassungsmöglichkeiten erforderlich, um nachhaltige Bewirtschaftungspläne zu entwickeln. Vor die-sem Hintergrund wurden in der vorliegenden Arbeit 59 langfristige Bergmischwald-Versuchsflächen entlang eines Höhengradienten in Europa untersucht. Der periodische jährliche Volumenzuwachs (iV) auf Bestandsebene, sowie die artspezifische Produktivitätsentwicklung in den letzten 30 Jahren bilde-ten den Schwerpunkt der Untersuchung. So konnte im Rahmen der Studie erstmals eine durchschnittli-che Produktivität der gemäßigten Bergmischwälder Europas ermittelt werden (9,3 m³ha-1 a-1 über alle Bereiche hinweg). Die Entwicklung zeigt, dass die Produktivität auf Bestandsniveau in den letzten Jahr-zehnten insgesamt konstant geblieben ist. Die artenspezifische Produktivitätsanalyse zeigt, dass der iV der Fichte zu Beginn der Studie (1980) noch etwa 14 m 3 ha-1 a-1 betrug und heute knapp 11 m 3 ha-1 a-1 beträgt. Mit knapp 7 m 3 ha-1 a-1 ist der iV der Tanne der niedrigste der drei Baumarten zu Beginn der Untersuchungsperiode. Das Wachstum der Tanne steigt jedoch signifikant auf über 11 m³ha-1 a-1 und ist damit heute die produktivste Baumart in den Berg-Mischwäldern Europas. Die Buche wächst über den gesamten Untersuchungszeitraum mit einer Wachstumsrate von ca. 8,2 m³ha-1 a-1. Der Rückgang der Produktivität der Fichte in den letzten 30 Jahren konnte somit durch eine Steigerung der Produktivität der Tanne weitgehend kompensiert werden und erklärt den konstanten iV auf Bestandsebene. Folglich konstatieren wir stabile Volumenzuwächse in Bezug auf den Klimawandel. Damit scheint eine kontinu-ierliche Versorgung mit Ökosystemgütern aus Berg-Mischwäldern gewährleistet zu sein. Summary Mixed mountain forests of Norway spruce (Picea abies (L.) Karst), silver fir (Abies alba Mill.) and Euro-pean beech (Fagus sylvatica) cover a total area of several million hectares in Europe. They connect the beech forest communities in the lowlands with the spruce-dominated alpine forest types. Due to their height zoning, these forests are particularly affected by climate change. In addition, new development techniques enable innovative possibilities for intensified mountain forest management. However, as little is known about the long-term development of the productivity of these forest systems in Europe, reliable information on productivity and adaptation options is required in order to develop sustainable management plans. Against this background, 59 long-term mixed mountain forest experimental plots along a height gradient in Europe were investigated in this study. The periodic annual volume increment (iV) at stand level as well as the species-specific productivity development over the last 30 years formed the focus of the study. For the first time, an average productivity of Europe's temperate mixed mountain forests (9.3 m³ha-1a-1 across all areas) could be determined within the framework of the study. This development shows that overall productivity at stand level has remained constant over the past decades. The species-specific productivity analysis showed that the iV of spruce at the beginning of Hilmers et al.: Zur Produktivität von Bergmischwäldern aus Picea abies, Abies alba und Fagus sylvatica in Europa DVFFA-Sektion Ertragskunde 25 Beiträge zur Jahrestagung 2018 the study (1980) was still about 14 m 3 ha-1 a-1 and today is just under 11 m 3 ha-1 a-1. With just under 7 m 3 ha-1 a-1 , the iV of fir is the lowest of the three tree species at the beginning of the study period. However , the growth of fir rises significantly to over 11 m 3 ha-1 a-1 and is therefore today the most productive tree species in the mixed mountain forests of Europe. Beech grows at a growth rate of approx. 8.2 m³ha-1 a-1 over the entire period under study. The decline in spruce productivity over the last 30 years has thus been largely compensated by an increase in fir productivity and explains the constant iV at stand level. Consequently, we observe stable volume increases in relation to climate change. This seems to guarantee a continuous supply of ecosystem goods from mixed mountain forests.
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Natural disturbances are among the most important factors that shape forest dynamics and forest landscapes. However, the natural disturbance regime of Norway spruce (Picea abies (L.) Karst.) forests in Europe is not well understood. We studied the disturbance regimes in three forest reserves in Bulgaria (Parangalitsa, Bistrishko branishte, and Beglika), which are representative of the range of conditions typical for P. abies ecosystems in central and southern Europe. Our data indicated that large-scale disturbances were most numerous in forests that were between 120 and 160 years old, those with unimodal diameter at breast height (DBH) distributions, and especially those located in vulnerable topographic settings. Wind disturbances ranged up to 60 ha, followed in one case by a 200 ha Ips typographus (Linnaeus, 1758) outbreak. Older forests and those with more complex structures (i.e., reverse-J DBH) were characterized by numerous small gaps but were also affected by a few larger disturbances. In some old-growth forests at highly productive sites, gaps could be so numerous that the long-term existence of old trees may become an exception. Over the past centuries, the natural range of variability of these Norway spruce forests in Bulgaria appears to have been shaped mostly by wind and bark beetle disturbances of various sizes. © 2015, National Research Council of Canada. All rights Reserved.
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Much of our understanding of natural forest dynamics in the temperate region of Europe is based on observational studies in old-growth remnants that have emphasized small-scale gap dynamics and equilibrium stand structure and composition. Relatively little attention has been given to the role of infrequent disturbance events in forest dynamics. In this study, we analyzed dendroecological data from four stands and three windthrow patches in an old-growth landscape in the Dinaric Mountains of Bosnia and Herzegovina to examine disturbance history, tree life history traits, and compositional dynamics. Over all stands, most decades during the past 340 years experienced less than 10% canopy loss, yet each stand showed evidence of periodic intermediate-severity disturbances that removed > 40% of the canopy, some of which were synchronized over the study area landscape. Analysis of radial growth patterns indicated several life history differences among the dominant canopy trees; beech was markedly older than fir, while growth patterns of dead and dying trees suggested that fir was able to tolerate longer periods of suppressed growth in shade. Maple had the fastest radial growth and accessed the canopy primarily through rapid early growth in canopy gaps, whereas most beech and fir experienced a period of suppressed growth prior to canopy accession. Peaks in disturbance were roughly linked to increased recruitment, but mainly of shade-tolerant beech and fir; less tolerant species (i.e., maple, ash, and elm) recruited successfully on some of the windthown sites where advance regeneration of beech and fir was less abundant. The results challenge the traditional notions of stability in temperate old-growth forests of Europe and highlight the nonequilibrial nature of canopy composition due to unique histories of disturbance and tree life history differences. These findings provide valuable information for developing natural disturbance-based silvicultural systems, as well as insight into maintaining less shade-tolerant, but valuable broadleaved trees in temperate forests of Europe.
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An intensive bark beetle outbreak occurred in 1993–1998 in the Tatra mountains between Slovakia and Poland. In the Slovak part of the outbreak practices consisted of: no action prior to 1994, intensive pest control management (trap trees, insecticides, salvage cutting) from 1995–1996, active differentiated approach (control measures according to the zonation of attacked stands) combined with intensive use of pheromone traps from 1997–1998. In Poland, the outbreak was mostly located in reserve areas where pest management or other activities were prohibited. Despite the use of intensive pest management measures, tree mortality was not significantly decreased in the Slovak region during the peak outbreak years of 1995 and 1996. Classical forest protection led to an increase in attractiveness of forest edges to bark beetles which could disperse to these areas from locations where no control measures were practiced. Unfavourable weather for bark beetles led to a rapid decrease in tree mortality in both parts of the study area.
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Forest insects and pathogens are the most pervasive and important agents of disturbance in North American forests, affecting an area almost 50 times larger than fire and with an economic impact nearly five times as great. The same attributes that result in an insect herbivore being termed a "pest" predispose it to disruption by climate change, particularly global warming. Although many pest species have co-evolved relationships with forest hosts that may or may not be harmful over the long term, the effects on these relationships may have disastrous consequences. We consider both the data and models necessary to evaluate the impacts of climate change, as well as the assessments that have been made to date. The results indicate that all aspects of insect outbreak behavior will intensify as the climate warms. This reinforces the need for more detailed monitoring and evaluations as climatic events unfold. Luckily, we are well placed to make rapid progress, using software tools, databases, and the models that are already available.
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Information on historical disturbances is vital to our understanding of current forest conditions. Dendro chronological methods provide one means of reconstructing disturbance histories in temperate and boreal forests. In particular, the dates of significant growth releases recorded on surviving trees provide strong inferential evidence of past disturbance events. The most common method of detecting releases (the percent-increase method) expresses the postevent growth increase as a percentage of the preevent rate. Despite its widespread use, the method is known to be overly sensitive at low rates of prior growth and overly stringent at high rates. We present an alternative method that directly follows the percent-increase method, but instead of dividing the postevent growth rate by the preevent rate, we simply subtract the two. If the difference exceeds a predetermined species-specific threshold, the event is considered a release. This absolute-increase method has convenient properties that remedy the shortcomings of the percent-increase method. We tested the validity of the absolute-increase thresholds by binary logistic regressions, and we compared the absolute- and percent-increase methods by various methods. We conclude that for the species evaluated in this study, the absolute-increase method represents an improvement over the standard percent-increase method.
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The Bavarian Forest National Park in Germany has experienced infestations of bark beetle (Ips typographus L.) since the 1980s, resulting in considerable ecological loss due to the destruction of almost 5800 ha of spruce forests. Although there have been numerous investigations on the physiology and ecology of the bark beetle, until now the spatio-temporal infestation and dispersal dynamics of the bark beetle over a longer period have still not been satisfactorily understood. The understanding of the structure and the dispersal of bark beetle infestations is however of significant importance for forest management systems in order to predict the risk of outbreaks, especially in the face of climate change.
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Structurally different from even-aged and balanced uneven-aged stands, irregular stands are an integral part of forested landscapes in northeastern North America. The maintenance or restoration of irregular stand structure may be desirable, especially in areas under ecosystem-based management. This can be achieved at the stand level through the implementation of irregular shelterwood systems. The objectives of this synthesis are to assemble the existing knowledge about the system, clarify the terminology in use, and discuss its place in silviculture in northeastern North America. Irregular shelterwood is compared with other regeneration methods and we propose a classification based on three variants. This silvicultural system is compatible with ecosystem-based management in forest types driven by partial stand mortality and gap dynamics and provides opportunities for maintaining old-growth forest attributes. However, it presents important challenges, especially with regards to planning, growth and yield prediction, and operational application.
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1Disturbance histories derived from old-growth forest remnants in Europe and eastern North America have shaped many of our current theories of forest dynamics and succession. Yet the small size typical of these remnants suggests they might not capture the full range of variability that may emerge at larger scales.2We investigated the frequency and severity of natural disturbance in a 2000-ha old-growth landscape (Big Reed Forest Reserve) in northern Maine, USA. Given its size, the Reserve provides an ideal opportunity to study, at multiple scales, natural forest processes in a region that has otherwise been dramatically altered by human activities. Using dendrochronological methods, we reconstructed disturbance histories for 37 randomly located plots stratified by five forest types (hardwood forests, mixed woods forests, red spruce forests, northern white-cedar seepage forests and northern white-cedar swamps).3We found no evidence of stand replacing disturbance on any plot during the last 120–280 years (depending on plot). The overall mean disturbance rate was 9.6% canopy loss per decade (median 6.5%, maximum 55%, plots pooled), yet the distribution was strongly skewed toward the lower rates.4We found little differences in disturbance rates between forest types, save a slightly lower rate in the northern white-cedar swamps. However, if we ignore forest-type classifications, we see that disturbance rates are clearly influenced by gradients in the relative abundance of component tree species, owing to species’ relative susceptibilities to particular disturbance agents.5Synthesis. Relatively low rates of canopy disturbance allow the accrual of shade-tolerant saplings. The abundance of this advance regeneration, coupled with the absence of stand-replacing disturbance, has maintained canopy dominance by shade-tolerant species in all plots, all forest types and throughout the entire landscape. Disturbance histories from individual plots coalesce to form a picture of a landscape in which pulses of moderate-severity disturbance are interposed upon a background of scattered small-scale canopy gaps. The landscape-level mosaic resulting from this disturbance regime consists of patches in various stages of structural development, not various stages of compositional succession.
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Summary 1 Data from elevations ranging from mixed hardwood-conifer forest at 600 m to subalpine Abies balsamea forest at 1120 m indicate that canopy gaps are not static but expand over time due to mortality of trees at the gap margin and coalescence of gaps. Gap expansion is more frequent than gap initiation. Ultimately such disturbance patches may become more extensive than is normally considered as typical of gap-phase disturbance, but the processes of development are the same. 2 Disturbance agents involved in gap initiation tend to differ from those involved in gap expansion. Spruce beetle, dwarf mistletoe and most root diseases predominate as agents of gap initiation, while windthrow/windsnap, chronic wind stress and Armillaria root disease are important agents of gap expansion. 3 Concepts of equilibrium gap-phase dynamics and a shifting-mosaic steady state do not fully account for the dynamics of these spruce-fir forests. A spruce beetle outbreak in the late 1970s/early 1980s killed most of a cohort of dominant, emergent Picea rubens . This epidemic initiated a long-term cycle of disturbance and release that is likely to be repeated in many years when a new cohort of P. rubens becomes sufficiently large to sustain another major bark beetle outbreak. 4 Episodic disturbance agents affect long-lived, dominant species at infrequent but regular intervals (up to hundreds of years) and operate at the landscape level. Gap-phase cycles appear to be nested within the long-term cycle. Over the long term, episodic dis- turbance drives such 'nested bicycle' dynamics. 5 Spatial and temporal distribution of disturbance results not only from stochastic events such as storms, but also from host specificity of agents of disturbance, their tendency to attack certain age classes of trees, local and regional contagion, and sus- ceptibility of trees at the edge of disturbance patches.
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The influence of natural disturbance on biodiversity is poorly known in the intensively cultivated landscape of Europe. As an example of insect disturbance we studied effects of gaps generated by outbreaks of the spruce bark beetle (Ips typographus) on biodiversity in the area of the National Park “Bavarian Forest” and compared them with openings (e.g. meadows) created by humans in these forests. Insects were sampled using flight interception traps across twelve ecotones between edges of closed forest, six bark beetle gaps and six meadows. The diversity and species density of true bugs and of bees/wasps increased significantly from the closed stand to the edge, and continued to increase inside the openings at interior and exterior edges. Species density in saproxylic beetles also increased significantly from closed forest to opening, but only across ecotones including bark beetle gaps. Similarly, the number of critically endangered saproxylic beetles increased significantly in bark beetle gaps. Using indicator species analysis a total of 60 species were identified as possessing a statistically significant value indicating preference for one of the habitat types along the ecotones: 29 of them preferred gaps, 24 preferred meadows, three were characteristic for edges of meadows, three for edges of bark beetle gaps, but only one was typical of closed forest. Most of our results support the thesis that I.typographus fulfils the majority of criteria for a keystone species, particularly that of maintenance of biodiversity in forests. Our results emphasize the value for the study and conservation of insect diversity of the policy of non-interference with natural processes pursued in some protected areas. As a recommendation to forest management for increasing insect diversity even in commercial forest, we suggest that logging in recent gaps in medium aged mixed montane stands should aim at retention of a part of the dead wood. Planting should be avoided, to lengthen the important phase of sunlit conditions.